I remember reading a short story in an anthology sometime between the end of the 90's and the 2000's. It was the French translation of an English story, thus it could be much older.
I remember the story being about a group of archaeologists excavating ruins and discussing why the galactic empire hasn't contacted them after the apocalypse. What the apocalypse was is not said, only to find out that there is no galactic empire: all the clues they had uncovered came from science-fiction books.
I believe they find out by uncovering an almost intact science-fiction pulp magazine from the 50's or 60's, but I could be mistaken.